The present invention relates to a method of and an apparatus for molding. More particularly this invention concerns the molding of a receptacle having an interior which is of considerably larger cross-sectional size than its mouth.
In the molding or casting of a receptacle such as a bottle whose mouth is of considerably smaller cross-sectional size than its interior, it is necessary to employ relatively complicated molding techniques. When the material being molded is of extremely high viscosity and has good surface tension it is possible to blow mold such a receptacle. Such blow molding is useful, for instance, when glass bottles are being made. Blow-molding equipment is comparatively expensive and its functioning is relatively complicated so that the cost of the finished product is somewhat high.
It is also known to centrifugally cast such articles. In this arrangement after the still-fluid hardenable material is introduced into the mold the mold is spun at high speed about its central axis. During such spinning the material is centrifugally pressed against the interior of the mold cavity. The spinning is continued until the material hardens into a receptacle having a hollow interior at the spinning axis. Such an arrangement not only requires relatively expensive casting equipment, but has the disadvantage that it is difficult exactly to control the shape of the hollow interior space inside the article being cast.
It has finally been suggested to provide a core for such devices. This core is invariably provided in several parts so that it can be pulled part-by-part out of the interior of the cast article once it has hardened. In practice such devices have not reached any wide degree of acceptance due to the complexity of operation and the considerable difficulty often encountered with extricating the multipart core from inside the finished article.